New York, Sept. 11 (Reuters): The United States, its forces on high alert at home and abroad, today solemnly and tearfully remembered the traumatic day one year ago when 19 young Arabs launched a carefully planned assault on America that killed 3,025 people.

On the anniversary of the September 11 attacks, virtually every town and city across the nation, every school and college, churches, synagogues and mosques as well as many factories and offices held ceremonies and observed a moment of silence for victims, young and old, from dozens of nations.

US military forces in West Asia went on top alert in response to warnings of possible terror attacks, some provided by a captured top official of Osama bin Laden’s al Qaida organisation that is believed to have masterminded last year’s attacks. In videos shot late last year, the Saudi-born bin Laden claimed advance knowledge of the attacks and praised their outcome.

President George W. Bush, speaking outside the newly rebuilt Pentagon facade, said the victims of September 11 did not die in vain and would be avenged.

“The enemies who struck us are determined and they are resourceful. They will not be stopped by a sense of decency or a hint of conscience. But they will be stopped,” he declared.

On a glorious sunny day eerily like the lovely morning of a year ago, tens of thousands of mourners that included bereaved family members, many clutching pictures of their loved ones, gathered with dignitaries, police officers marching in formation and carrying flags, troops wearing combat fatigues, fire fighters, religious leaders and survivors. They gathered at the strangely sterile void in bustling lower Manhattan that used to be the site of the tallest skyscrapers in New York City.

Bagpipers played a dirge and then fell silent and came to attention at 8.46 a.m. (1246 GMT) — the moment the first plane hit the north tower of the World Trade Center, turning a beautiful late summer morning into an inferno, trapping thousands of people in a burning tomb from which there would be no escape.

A banner draped over the site read:“We will never forget.” Accompanied by cellist Yo-Yo Ma playing a Bach partita, former New York Mayor Rudolph Giuliani began a reading of the names of each of the 2,801 victims of the World Trade Center.

The reading was interrupted by the tolling of bells at 9.03 am (1303 GMT), marking the moment when the second plane struck the south tower.

As they listened, family members and friends descended into Ground Zero to lay flowers at the site. Some clutched pictures, and others held young children tightly. Some were stoic, but many wept seemingly inconsolably.

Less than an hour later just outside Washington DC, ceremonies began at the Pentagon where 189 people died. Another solemn remembrance soon followed near Shanksville, in the placid countryside of western Pennsylvania, where a bell tolled 45 times for each person who died after refusing to allow hijackers to steer the plane they had commandeered to its presumed target in the US capital.

“In the air, a wave of courage made its way from the cockpit to the rear of the aircraft and back again, with all persevering to the end,” Sandy Dahl, widow of pilot Jason Dahl, told a crowd of mourners and local residents. Bush arrived at the site early in the afternoon to console family members of the victims and lay a wreath.

The ceremonies were choreographed to echo the horrific unfolding of events a year ago. Bells tolled again in New York at 9.59 am (1359 GMT), marking the moment when the south tower of the World Trade Center collapsed, sending a massive cloud of smoke and ash spiralling high into the sky, blanketing most of lower Manhattan in a choking fog of destruction. The north tower collapsed exactly half-an- hour later.

The United States was on its second highest state of alert in response to intelligence that suggested new attacks were possible.

Attacks on three US bases in Afghanistan today caused no injury or damage. The assaults highlighted continued instability in Afghanistan 11 months after US forces attacked bin Laden’s al Qaida network and drove the Taliban movement, its Islamic backers, from power.